Synaptic transmission at many central and peripheral cholinergic synapses is mediated by nicotinic acetylcholine receptor channels (nAChRs). Nicotinic AChRs at neuronal synapses (unlike those at the neuromuscular junction) are apparently comprised of only two types of subunits: ligand binding (alpha) and structural (beta). Recent molecular and biophysical studies indicate diversity in both the sequences of alpha and beta subunit genes expressed in the nervous system as well as in the functional properties of nAChR channels. Thus, to date four different alpha and three different beta subunit transcripts have been identified in neural tissue. Our preliminary functional studies on particular central and peripheral neurons indicate that as many as four distinct nAChR channel types are expressed by individual neurons and that the functional classes of nAChRs expressed are regulated during the embryonic development. The relationship between the sequence diversity of nAChR subunit genes and functional properties of neuronal nAChRs is unclear. The primary goals of this proposal are to determine how the diversity in nAChR subunit sequences relates to the different functional classes of nAChRs expressed and how this receptor diversity is regulated by synaptogenesis. We propose to study nAChRs in specific central and peripheral cholinoceptive neurons (those of the medial habenula and lumbar sympathetic chain, respectively) that are readily identified from early developmental stages in vivo and that can be removed and innervated by the appropriate synaptic input for detailed study in vitro. We will combine biophysical and molecular techniques to: 1) determine the cellular pattern of nAChR subunit gene expression during development and to examine whether there are correlative changes in the classes of nAChR channels expressed 2) examine the influence of innervation and denervation on the types of nAChRs subunit genes and nAChR channels expressed and 3) examine the role of individual subunits in the expression of specific functional classes of nAChRs. The recent in situ hybridization studies reveal that central nicotinic pathways are considerably more extensive than previously appreciated. Complimentary functional studies are largely lacking. The proposed studies will constitute the first such combined analysis of receptor subunit expression and channel function in the same neurons. Since the physiological roles subserved by the neuronal populations chosen for study are so diverse, these studies are likely to reveal important differences n the mechanisms of regulation of nAChRs in the central vs peripheral nervous system.